BJA Advance Access originally published online on March 18, 2005
British Journal of Anaesthesia 2005 94(6):800-804; doi:10.1093/bja/aei115
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Bispectral index monitoring may not reliably indicate cerebral ischaemia during awake carotid endarterectomy
1 Department of General Anesthesiology, Cleveland Clinic Foundation, Cleveland, OH, USA. 2 Division of Neurosurgery, Department of Surgery, 3 Department of Anaesthetics and 4 Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, UK
* Corresponding author: Department of Neurosurgery, Newcastle General Hospital, Westgate Road, Newcastle upon Tyne NE4 6BE, UK. E-mail: a.d.mendelow{at}ncl.ac.uk
Background. Intraoperative ischaemia during carotid cross-clamping in patients undergoing carotid endarterectomy (CEA) is a major complication and prompt recognition of insufficient collateral blood supply is crucial. Electroencephalogram (EEG) is believed to be one of the useful forms of monitoring cerebrovascular insufficiency during CEA. The aim of this study was to evaluate the utility of bispectral index (BIS) monitoring, a processed EEG parameter, for the reliable detection of intraoperative cerebral ischaemia during awake CEA.
Methods. We monitored 52 patients continuously with the BIS monitor together with assessment of neurological function (contralateral upper and lower limb strength and the verbal component of the Glasgow Coma Scale for speech) in patients undergoing awake CEA.
Results. Overall mean BIS value in all patients was 96 (SD 2.9). In five patients who showed clinical evidence of cortical ischaemia during carotid cross-clamping, there was no change in the original range of BIS values throughout the procedure (96.7 [3.2]). In one patient BIS values decreased to 38 about 5 min after the incision and recovered within the next 10 min. The mean BIS value in the remaining 46 patients who did not develop clinical signs of ischaemia was 95.4 (2.6). Three cases are presented which demonstrate the inability of the BIS monitor to detect cerebral ischaemia.
Conclusions. Lack of correlation of BIS with the signs of cerebral ischaemia during CEA makes it unreliable for detection of cerebrovascular insufficiency. We conclude that awake neurological testing is the preferred method of monitoring in these patients.
This study was conducted in the Department of Neurosurgery, Newcastle General Hospital, Newcastle Upon Tyne NE4 6BE, UK. Preliminary results were presented at the British Neurosurgery Research Group Meeting, Sheffield, March 29–30, 2001.
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